In general, a manual or automatic vehicle transmission includes a number of torque transmitting devices (referred to herein as clutch assemblies). Hydraulically controlled clutch assemblies can be configured with compliance enhancing devices such as a hydraulic accumulator with a damper. Dampers are typically configured to absorb excessive pressure pulses upon abrupt rises in the apply pressure which governs the piston of the clutch assembly. The damper may include a mechanical spring or other energy absorbing device. Dampening is most desirable to improve shift feel as the transmission shifts from one gear to the next.
The process of shifting from one gear to another gear occurs in three distinguishable phases: a) fill phase; b) torque phase and c) inertia phase. During the torque phase in power-on up-shifts, the torque is transmitted from the off-going clutch to the on-coming clutch until the torque is substantially transferred from one clutch to the next. Thereafter, the gearing shifting process enters into the inertia phase, where the slip speed of the on-coming clutch progresses to zero. The torque phase is preceded by a fill phase of which oil is supplied to the on-coming clutch. It is desirable to have a smooth transition during torque phase because gradually applying the piston will produce a smooth transference of torque. Conversely, abruptly applying the piston will produce an irregular transference of torque that may be detected by the vehicle operator. Therefore, an active compliance element in the on-coming clutch hydraulic control system is highly desirable during power-on up-shifts. However, during power-on down-shifts the off-going clutch is released in a precisely controlled manner and the on-coming clutch is sought to be rapidly disengaged and the inclusion of the compliance element slows the pressure response speed.